1. Field of the Invention
The present invention relates to a method of using memories, notably in aid of vehicle navigation, in which a bidirectional link is provided between a transmitter/receiver with a memory, called local memory and a server with a memory called central memory. The memories contain, inter alia, geographical data such as type and number of road, place, direction.
The invention also relates to a system including user information means, a processor for controlling said information means, and a message transmitter/receiver capable of having a dialog with a remote central database under the supervision of the processor for requesting and obtaining information.
2. Description of the Related Art
A navigation system for vehicles that makes use of a bidirectional link is known from document DE 196 08 538. According to this document, the system receives by means of a receiver encrypted information targeted as a function of the position of the transmitter, and transmits to a central database via a transmitter a request for a key to decode the encrypted information.
A disadvantage of such systems is their relative slowness and possible cumbersomeness of the transmission channels and the cost of transmissions; because the information is sent to the users in full.
In an embodiment of the invention, within the framework of a particular message coding mode, to provide a system that performs better and saves memory space.
For this purpose, with a message being received in the form of reference numbers each denoting a standard message element supposed to be present in a local database, then a message comprising reference numbers is received, the standard message elements corresponding to the reference numbers are searched for in the local database and, if one of them is not there, a call from the server is launched and the latter transmits the lacking element in response, and the message is processed thereafter.
In a system, with a message being received in the form of reference numbers each denoting a standard message element so that the processor is supposed to find in the local database the standard message element corresponding to a reference number as a function of the received reference number, the local database includes a limited quantity of standard message elements so that, for certain reference numbers, the corresponding message element is not present in the local database, and the processor includes means for starting a dialog by means of the transmitter/receiver between itself and the central database so as to obtain the lacking standard message element corresponding to the reference number.
Particular embodiments of the invention are described hereinafter.
These aspects of the invention as well as other more detailed aspects will appear more clearly regarding to the following description of a preferred embodiment constituting a non-limitative example.